The present invention generally relates to centrifuges and in particular to centrifuges enabling automatic discharge of solids that accumulate during separation.
Many different types of centrifugal separators are known for separating heterogeneous mixtures into components based on specific gravity. A heterogeneous mixture, which may also be referred to as feed material or feed liquid, is injected into a rotating bowl of the separator. The bowl rotates at high speeds and forces particles of the mixture, having a higher specific gravity, to separate from the liquid by sedimentation. As a result, a dense solids cake compresses tightly against the surface of the bowl, and the clarified liquid, or “centrate”, forms radially inward from the solids cake. The bowl may rotate at speeds sufficient to produce forces 20,000 times greater than gravity to separate the solids from the centrate.
The solids accumulate along the wall of the bowl, and the centrate is drained off. Once it is determined that a desired amount of the solids has been accumulated, the separator is placed in a discharge mode in which the accumulated solids are removed from the separator. In a typical configuration, an internal scraper is engaged to scrape the solids from the walls of the separator bowl.
Prior separators have shortcomings when operating with particular kinds of materials. For example, many separators may not be capable of completely discharging residual solids that are sticky, which can result in poor yield. This can be especially problematic for high-value materials such as are encountered in pharmaceutical processes. Additionally, many separators subject the feed material to very high shear forces when accelerating the feed liquid to the rotational speed of the bowl, which can damage sensitive materials such as biological substances that include intact cells.
It would be desirable to have a centrifugal separator that can be effectively used with materials of the type described, namely those that result in sticky accumulated solids and those that are sensitive to shear forces generated during the centrifuge process.